When light strikes the boundary between two media at an angle greater than the critical angle, and it is moving from a medium with a higher refractive index to one with a lower refractive index, total internal reflection occurs.
In this case, no light passes into the second medium. Instead, the entire light wave is reflected back into the first medium. This reflection is not partial like in normal reflection; it is 100%, meaning all the light energy stays in the original medium.
This phenomenon only occurs when:
- Light travels from a denser (optically) medium to a rarer one.
- The angle of incidence exceeds the critical angle specific to the pair of materials.
Total internal reflection is used in applications like optical fibers, prisms, periscopes, and binoculars, where keeping light contained or redirecting it efficiently is essential.